A Randomized, Masked Study of Triiodothyronine Plus Thyroxine Administration in Preterm Infants Less Than 28 Weeks of Gestational Age: Hormonal and Clinical Effects

Abstract

A randomized, placebo-controlled, masked study was conducted of the responses of thyroid parameters, cortisol, and the cardiovascular system to a single dose of triiodothyronine (T3) 24 h after birth, followed by a daily dose of thyroxine (T4) during 6 wk to infants <28 wk gestational age. Thirty-one infants were assigned to three groups: 1) group A: T3 24 h after birth plus daily T4 during 6 wk; 2) group B: placebo T3 and T4 during 6 wk; and 3) group C: placebo T3 and placebo T4. T4, free T4, T3, free T3, reverse T3, thyroid-stimulating hormone, and cortisol were measured in cord blood and on days 1, 3, 7, 14, 21, 42, and 56. Data on pulse rate, blood pressure, and cumulative dose of inotropic agents were collected. T3 (0.5 μg/kg) resulted in a plasma increase until day 3. Thereafter, plasma T3 levels were comparable between the groups. T4, free T4, and reverse T3 were increased in groups A and B during the period of T 4 administration. Thyroid-stimulating hormone suppression was of shorter duration in group A. T3 and T4 administration did not have any effect on cortisol levels. We did not find any effects of T 3 or of T4 administration on the cardiovascular system. A single injection of T3 (0.5 μg/kg) given 22-26 h after birth only leads to a 2-d increase of T3 levels and does not have effects on the cardiovascular system. This study does not support the use of T3 according to our regimen in preterm infants.